Dia , Though the size of breast depends on various factors like genetics , body mass and proportion, fat contents and physical activity etc. and hence It Is multifactorial . Similarly treatment or breast enhancement also depends on the various factor. Considering your age of 26 yrs and ht 5.3 and weight 49kgs. Some of Hormonal therapy will be advantageous . Breast enhancement massage oil and oral medications have also shown positive report in patients and can be beneficial to you .Considering your age it will show fast and good  results. Consult me here on practo.

Breast cream and breast message may be helpful Breast implants surgery is also advisable

Please consult a plastic surgeon

Surgery. But it can also have side effects.

Consult with a surgeon